The field of this invention is methods of manufacturing heat exchangers, and, more particularly, those employing arrays of parallel, single-wall tubes. The technique disclosed is particularly well suited for the Microtube-Strip (MTS) design of Doty, U.S. Pat. No. 4,676,305, but it is also advantageous in numerous other designs.
The instant invention pertains to a method of assembling a plurality of microtubes rigidly into position so as to facilitate their rapid interference pressing into metallic header tubestrips. As such, this invention is distinguished from numerous patents that pertain to tube welding techniques or chamber forming techniques or manifolding techniques.
This invention allows a reduction in the cost of tube alignment, insertion, and welding to typically less than one U.S. dollar (1988) per 100 tubes, compared to the current typical manufacturing costs of 100 to 1000 times that amount for typical heat exchangers. This invention permits tube alignment, insertion, and welding rates to exceed many hundreds of thousands of pieces per day per production line.
The instant invention utilizes fusible alloys in the common manufacturing usage: alloys with relatively low melting points that are intended to be repeatedly solidified and reheated for temporary manufacturing purposes. Fusible alloys are substantially from the following elements: bismuth, lead, tin, cadmium, indium, zinc, silver, and antimony. Melting points of the common fusible alloys range from about 46.degree. C. to about 222.degree. C., but those alloys with liquidus points below 105.degree. C. are best suited for rapid cycling applications employing water cooling. They are also less prone to wet the surface of and form metallurgical bonds to the microtubes and fixtures. Several examples of such alloys are: (1) 44.7% Bi, 22.6% Pb, 8.3% Sn, 5.3% Cd, 19.1% In, eutectic at 46.8.degree. C.; (2) 50.7% Bi, 30.9% Pb, 15% Sn, 3.4% Cd, solidus 70.degree. C., liquidus 84.degree. C.; (3) 52.5% Bi, 32% Pb, 15.5% Sn, eutectic at 95.degree. C.
Marco, U.S. Pat. No. 3,364,548, discloses the use of sacrificial tooling in a method of producing electroformed heat exchangers with at least two independent fluid flow chambers by means of reactive metals, electroplating, masking, and chemical etching. Such a technique is relatively slow, costly in materials and supplies, and environmentally hazardous, and it does not address the problem of high speed assembly of millions of microtubes.
Holmes, U.S. Pat. No. 3,961,010, uses fusible alloys to hold tubes in position and to occupy space in a method of forming heat exchanger arrays and headers by means of plastic injection molding. Frei, U.S. Pat. No. 4,117,884, uses pins and strips to position and space 6 mm to 12 mm glass tubes to allow elastomeric headering. Kerr et al, U.S. Pat. No. 4,578,850, uses resilient, elastomeric gaskets, sandwiched captive between metal header plates, to eliminate tube welding. Such techniques are not applicable to high temperature exchangers and do not adequately address the problem of high speed assembly. Moreover, the techniques of Frei and Kerr are not usable with microtubing.